n [ U ] ( BrE )
a hobby in Britain, popular mainly with boys but also with some adult men. It involves going to places where trains can be seen, especially railway stations, and collecting the numbers of railway engines they see by writing them down. People sometimes make fun of this hobby and the people who do it because they think it is a boring and ridiculous thing to do:
John goes trainspotting every weekend.
► trainspotter n
a person whose hobby is trainspotting.